1. Field of the Invention
The present invention concerns a material supply and melting method in the case of molding by injection molding low melting point metal molds of zinc, magnesium or their alloy or the like with low melting point.
2. Detailed Description of the Prior Art
Die cast is adopted for casting nonferrous metals of low fusion point, die cast requires a smelter for melting metal material completely, and the casting is executed by drawing molten metal from this smelter or extruding by a plunger. The dipping of molten metal for molding is dangerous, and the extrusion molding by plunger of the prior art presents problem of low weighing accuracy of molten metal; therefore, the Inventors have developed a molding machine capable of molding high quality metal products under an safe operation, by injection filling of a mold with weighed molten metal, similarly as plastic material injection molding.
This novel metal material molding machine is composed to nozzle-touch a nozzle member of the nozzle-touch block front to a die of a die squeeze mechanism, to nozzle-touch a nozzle portion at the extremity of a melting vessel composing the body of an injection mechanism to this nozzle-touch block, to weigh metal material in the melting vessel, molten by an external heat, by retrogression of an internal injection plunger, and to fill the die by injection from the nozzle member, trough a hot runner in the nozzle-touch block, by forward movement of this injection plunger.
It is necessary to maintain the accumulation amount and the temperature of molten metal constant, in order to obtain metal molds of stable quality by such a molding machine; therefore, it must be able to control the supply amount of metal material to an amount corresponding to the accumulated amount and, if the accumulated amount is insufficient, to maintain the accumulation amount and the temperature constant, by compensating immediately without being limited by the progress of molding process.
The present invention, devised considering the situation mentioned above, has an object of providing a material supply and melting method in injection molding of molten metal, allowing to maintain the accumulation amount and the temperature of molten metal constant all the times, by taking the temperature as reference when the operation starts, and the accumulated amount as reference during the molding operation.
In order to attain this object, the present invention is a method for supplying granular metal material from a supply apparatus into a cylindrical melting vessel having on the extremity thereof a weighing chamber communicating with a nozzle member and a rotatable agitation means inside and an injection means formed into an injection plunger on the extremity portion thereof and being inserted advanceably and retractably into a center portion of the agitation means, said injection plunger being slidably engaged with the weighing chamber, comprising the steps of: melting the metal material by an external heat, accumulating, weighing, then injecting and charging into a mold by the injection means to mold a metal mold, wherein the supply apparatus and the agitation means of metal material at the moment of operation starting are controlled to be inactive until the temperature of the melting vessel attains a predetermined value and to start operating when the predetermined temperature is attained, allowing to supply and agitate the metal material, and the supply apparatus and the agitation of metal material after the predetermined temperature is attained, are performed by gradually supplying and agitating, until metal material of at least 6 times or more of the maximum injection volume is accumulated in melt state.
Moreover, the invention is a method, wherein the speed and the time of the supply apparatus are controlled so that the supply of the metal material during the molding operation starts after the weighing completion in the duration of the operation of the agitation of molten metal in the melting vessel by the agitation means and stops the metal material for one shot of mold including spool, runner or others before starting the following weighing, for maintaining the accumulation amount and the temperature of molten metal in the melting vessel constant all the times.
Further, the invention is a method, wherein the supply apparatus is controlled so that the supply of the metal material during the molding operation starts when the molten metal surface level is lowered to the lower limit of the predetermined level value, by monitoring and detecting the variation of the molten metal surface level by a liquid level sensor in the duration of the operation of the agitation of molten metal accumulated in the melting vessel by the agitation means, and stops when the upper limits is attained, for maintaining the accumulation amount and the temperature of molten metal in the melting vessel constant all the times.